Careful morphologic analysis of transmural coronary artery pathology and vessel wall geometry would provide important insights for new transcatheter techniques to recanalize obstructed coronary and peripheral vessels. Specifically, plaque eccentricity, global and regional thickness of the underlying media, and cross sectional dimensions of plaque and vessel area would be important to determine in patients with severe atherosclerosis. We examined the coronary architecture from 21 neocropcy patients with severe atherosclerosis and 9 control patients with minimal atherosclerosis and no cardiac symptoms using a computerized video planimetry system of transverse histologic sections. We found attenuation of the media consistently in patients with progressive atherosclerosis with areas of focal thinning in regions of greatest plaque accumulation. In addition, compensatory vessel wall dilatation appears to be a uniform response to progressive plaque accumulation. However, those individuals with greatest lumen compromise lacked adequate compensatory vessel wall dilatation which appeared to be responsible for cross sectional narrowing. Thus, absolute plaque area was not greatly increased in regions of severe stenosis compared with contiguous more normal vessel segments. This finding has important implications in the pathophysiology of hemodynamically significant and clinically active coronary artery disease. If such observations are corroborated, angiographically significant and clinically symptomatic coronary artery disease is due largely to absent or diminished compensatory vessel dilatory responses and not focal increase in plaque deposition. These findings will have important implications in further understanding current pathophysiology and in devising treatment strategies including ablative recanalization techniques.